This the one, the only 10-star add-on.
5 stars for the value of its mission
5 stars for execution
Firefox has some work to catch up to where it was before, but it can still handle this add-on quite well. Visual, collapsible tab tree just makes the browsing experience so much more sensible.
I'm looking forward to seeing the weird old tab bar disappear again, but that's a problem with WE not with this add-on.
I can hardly remember a time I was this happy with a browser feature since the invention of the DOM inspector.

most valuable firefox extension, and in fact the only reason to use firefox. thank you!!!

yo! I second "Can't live without it"
Thanks a LOT for this awesome extension.
Several years ago (about 6 i think), the sudden inspiration crossed my mind, that tabs should not be listed horizontally, and after some longer research at that point in time (treestyletab was lesser known), i found this and was happy EVER AFTER.
It's pretty incredible that the devs made this working with firefox Quantum out of the box, I can't believe the effort.
I just wanna say: Thank you!
And you don't even want Donations, tears in my eyes, much love :)

TST is the reason I've never even considered switching to using another browser. Works perfectly on FF57. Thank you so much for all your hard work!

Thank you for this very useful addon, cannot use browser without it.

Splendid job on converting to Firefox Quantum. With the changes to chrome.css from the wiki, it looks great!

Perfect when opening lots of tabs on a widescreen monitor. All tabs remain readable contrary to the normal tab layout.

if not this plug-in I'd give up using FF and go for Chrome!

This is must have extension. It would be even greater if it could work in tandem with ColorfulTabs.

Just to remind older comments. One can hide FireFox tab bar and Side Panel title with userChrome.css file like that:

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

/* to hide the native tabs */
#TabsToolbar { visibility: collapse; }

/* to hide the sidebar header */
#sidebar-header { visibility: collapse; }

The best vertical tabs solution. I cannot use Firefox without it.

After Firefox killed TabMixPlus I thought I would have to switch to another browser. Eventually I found Tree Style Tab, which is even better. Now I just wish I had a way to turn off Firefox's own tabs, since they are so lacking in features as to be almost useless.

Pretty happy with this after doing some of the "Advanced" style customizations that the author suggests on the wiki. This is a much better tree-tab experience than anything I was ever able to achieve with Chrome (Sidewise is the best I found there).

Dear Piro,
Thank you for making something that works with Firefox 57! I know you're doing the best you can with the limitations, and thank you for the helpful information on the Wiki!